A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been attempted. The electromagnetic induction refers to a phenomenon in which a voltage is induced so that a current flows when a magnetic field is varied around a conductor. Although the commercialization of the electromagnetic induction technology has been rapidly progressed around small-size devices, the power transmission distance thereof is short.
Until now, the long-distance transmission using the electromagnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.
Recently, an energy transfer scheme has been extensively used based on the magnetic resonance among wireless power transmission schemes.
Since a wireless power transmission system based on the electromagnetic induction scheme and the resonance scheme wirelessly transmits electrical signals generated from transmitter and receiver sides through a coil, a user can easily charge an electronic device such as a portable device with electricity.
The wireless power transmitting apparatus produces AC power having a resonance frequency and transmits the AC power to the wireless power receiving apparatus. In this case, power transmission efficiency is determined due to various causes. Meanwhile, the demand for the improvement of the wireless power transmission efficiency is increased.